“Like” it or not, you consented to Facebook’s sociological experiment.

You’ve probably already heard about the controversial study that manipulated the Facebook feeds of nearly 700,000 users to study the social network’s emotional impact. But as far as the researchers were concerned, everyone agreed to participate by virtue of having a Facebook account.

The researchers from Facebook and Cornell University never actually read any posts, but they did alter the news feed algorithm for 689,003 users to skew the presence of positive or negative posts. They then tracked subsequent posts from those users by using positive or negative keywords.

“As such, it was consistent with Facebook’s Data Use Policy, to which all users agree prior to creating an account on Facebook, constituting informed consent for this research,” read the study, which was published in the Proceedings of the National Academy of Sciences.

Here’s the line in the policy that Facebook says allowed it to manipulate the feeds without telling users before, during or after the study took place for a week in January of 2012:

“[I]n addition to helping people see and find things that you do and share, we may use the information we receive about you…for internal operations, including troubleshooting, data analysis, testing, research and service improvement.”

This is where the “ethical conundrum” begins, said bioethicist and lawyer Leslie Meltzer Henry, who works at the Johns Hopkins Berman Institute of Bioethics and the University of Maryland Carey School of Law.

“The type of one-click consent that Facebook users provide when they agree to the site’s data use policy is very different from the type of informed consent that’s ethically and legally required” of most biomedical or behavioral studies, said Meltzer Henry, adding that one-click-consent “is inadequate to cover the potential harm” that can come from participation in a study that involves emotional manipulation.

Institutions that receive federal funding are required to abide by a federal policy called the “Common Rule,” which protects human experiment subjects by ensuring that they know about the study and that they understand the risks involved. It also requires institutional review boards at universities and hospitals to approve the way subjects of biomedical or behavioral studies are treated.

Although Facebook is private, and therefore not subject to the Common Rule, two of the three researchers who designed the study worked at Cornell University, which is subject to it. And the journal where the study was published, called the Proceedings of the National Academy of Sciences, requires studies to go through institutional review boards, too.

Susan Fiske, the Princeton University psychology professor who edited the study for the journal said she was concerned about the ethics of the study as well, but she put her faith in Cornell’s and Facebook’s institutional review boards.

“According to the authors’ revision cover letter to me, the Cornell [institutional review board] classified the research as exempt because it was a ‘pre-existing dataset’ (presumably, Facebook’s anonymized data),” Fiske wrote in an email to ABC News.